The scoop on bullet wounds is very simple: fired from a long distance, the bullet enters an object making a small entry wound, usually the size of the bullet, and leaves the object with an exit wound the same size or, usually, larger. From the medical website “Explore Forensics“:
Exit wounds – as we have already mentioned – are usually larger than the entrance wound and this is because as the round moves through the body of the victim it slows down and explodes within the tissue and surrounding muscle. This slowing down of the projectile means that as it reaches the end of its trajectory it has to force harder to push through. This equates to the exit wound normally looking larger and considerably more destructive than its pre-cursor – the entrance wound. Exit wounds will often bleed profusely as they are larger, but entrance wounds can sometimes look only like small holes…
JFK had the back of his head blown off, as seen in Abraham Zapruder’s film (recall Jackie climbing behind the back seat in the heat of the moment to retrieve a large part of her husband’s skull). Now one of the surgeons, who held Kennedy’s head in the Operating Room at Parkland Hospital, confirms that the back of the head was missing. That this was an exit wound. Dr. Robert McClelland further says a colleague, who spoke to the press, was threatened at the time by the Secret Service and never spoke of the assassination again.
The President’s vehicle was moving slowly before the shot, so momentum from the car would not propel the large skull fragment backwards with such force. Two incontrovertible facts: The fragment went backwards, and the posterior skull wound was much larger than the entrance wound, confirm that Kennedy was shot from the front, not the rear. Not from behind, where the Texas School Book Depository was located. Possibly from the grassy knoll.
There is controversy about the Xrays, autopsy, and about so much else. But the laws of physics are inviolable. The shot that blew off President Kennedy’s posterior skull did not originate from the School Book Depository.